Question: Solve for $x$ and $y$ using substitution. ${x+3y = -7}$ ${x = -2y-4}$
Since $x$ has already been solved for, substitute $-2y-4$ for $x$ in the first equation. ${(-2y-4)}{+ 3y = -7}$ Simplify and solve for $y$ $-2y-4 + 3y = -7$ $y-4 = -7$ $y-4{+4} = -7{+4}$ ${y = -3}$ Now that you know ${y = -3}$ , plug it back into $\thinspace {x = -2y-4}\thinspace$ to find $x$ ${x = -2}{(-3)}{ - 4}$ $x = 6 - 4$ ${x = 2}$ You can also plug ${y = -3}$ into $\thinspace {x+3y = -7}\thinspace$ and get the same answer for $x$ : ${x + 3}{(-3)}{= -7}$ ${x = 2}$